1. Technical Field
The present invention relates to time-calibration circuits and more particularly to a real-time-calibration circuit for multiple CPUs.
2. Description of Related Art
A real-time clock is known to being used in electronic devices such as personal computers, mobile phones, and servers, for getting the actual time. Generally, the conventional real-time clock is electrically connected with a CPU of the electronic device or built directly in the CPU. Where the electronic device has plural CPUs, theses CPUs usually each have a real-time clock for timing independently. Also, peripheral apparatuses for the electronic device usually each have a real-time clock for getting the actual time.
FIG. 1 shows a conventional circuit for controlling real-time clocks of multiple CPUs. In a conventional electronic device, the CPUs 1, 4, 7 function as a communication means, a control means and a panel board, respectively. Therein, CPU 1 is further connected with an external network 200. The CPUs 1, 4, 7 each have a real-time clock 2, 5 or 8 built therein. The real-time clocks 2, 5, 8 work for getting the actual time independently. However, differences are likely to exist among the results of the real-time clocks 2, 5, 8, and such differences can accumulate over time to the extent that the operation of the electronic device is adversely affected. For performing time calibration on the real-time clocks 2, 5, 8, the real-time clocks 2, 5, 8 have to be calibrated one after another, and this process may interference the communication among the CPUs 1, 4, 7. Moreover, for allowing the real-time clocks 2, 5, 8 to remain running with the correct time after the electronic device is turned off or unpowered, the real-time clocks 2, 5, 8 have to be connected with batteries 3, 6, 9. These batteries increase the manufacturing costs of the electronic device. In view of this, the inventor of the present invention makes improvement to the conventional real-time clocks by providing the present invention.